In many areas of industrial metrology, it is necessary to check bores in workpieces with respect to their shape accuracy. It is in particular necessary to determine deviations from a predefined shape, in addition to a circular shape or an ellipse, a star shape or a freeform shape, to mark the respective workpiece as unusable as required. The shape accuracy of bores can in principle be determined by means of shape measurement devices and/or 3D coordinate measurement machines in a laboratory-like measurement room. Such shape determinations are, however, relatively time-consuming and very expensive due to the high purchasing costs for the measurement devices. In addition, the corresponding measurements can easily be influenced by changing environmental conditions such as temperature, contaminants, vibrations and the like. For these reasons, a complete inspection, in which all workpieces produced are checked, can hardly be carried out in the named manner.
If the roundness in a circular bore should be checked, in practice the “ovalness” of a bore is frequently determined instead of the roundness as an approximated value for the roundness deviation. The ovalness can be determined via a diameter determination. If the shape error is distributed symmetrically along the bore circumference, the ovalness generally sufficiently corresponds to the roundness deviation. If, however, an asymmetrical circular deformation is present, there are considerable deviations between the ovalness and the roundness deviation. This can have the result that under certain relationships of the diameter tolerance and roundness tolerance the ovalness is not a suitable test criterion for the division of the workpieces into the categories “usable” and “non-usable”. Quality control may have to be supplemented by supporting roundness measurements carried out in the measurement room, which is in turn associated with a high time effort and unwanted costs. Since the roundness determined via the ovalness is smaller in many practical cases than the directly determined roundness, there is in particular the problem that workpieces which are unusable due to inadmissibly large shape errors are classified as usable, which generally should be avoided.